WO2018095405A1

WO2018095405A1 - On-line input and quit control method and device for voltage-source converter unit

Info

Publication number: WO2018095405A1
Application number: PCT/CN2017/112844
Authority: WO
Inventors: 鲁江; 卢宇; 董云龙; 汪楠楠; 王永平; 赵文强; 田杰; 李海英
Original assignee: 南京南瑞继保电气有限公司; 南京南瑞继保工程技术有限公司
Priority date: 2016-11-25
Filing date: 2017-11-24
Publication date: 2018-05-31
Also published as: RU2714121C1; US10797487B2; US20190252885A1

Abstract

Provided is an on-line input and quit control method for a voltage-source converter unit. The method achieves the on-line input of a voltage-source converter unit by means of performing steps, such as charging control, unlocking transfer control and operation adjustment control, on a voltage-source converter to be input, and achieves the on-line quitting of the voltage-source converter unit by means of performing steps, such as direct-current voltage reduction control, bypass transfer control and converter locking control, on a voltage-source converter to be quit. Correspondingly, provided is an on-line input and quit control device for a voltage-source converter unit, which can achieve the on-line steady input and quitting of a voltage-source converter in a series-type hybrid direct-current power transmission system or a series-type flexible direct-current power transmission system, without affecting the normal and stable operation of other already running converters.

Description

Method and device for online input and exit control of voltage source converter unit

Technical field

The invention belongs to the technical field of direct current transmission, and particularly relates to a method and device for online input and exit control of a voltage source converter unit.

Background technique

HVDC transmission systems can be divided into two types: conventional direct current transmission systems based on thyristor converters (LCC-HVDC) and flexible direct current transmission systems based on fully-regulated voltage source converters (VSC-HVDC). The conventional DC transmission system has low cost, low loss and mature operation technology. Most of the DC transmission systems currently in operation in the world are LCC-HVDC systems, but the conventional DC transmission system is prone to commutation failure and AC exchange on the inverter side. The system has strong dependence, needs to absorb a large amount of reactive power, and has a large area of converter station. The new generation of flexible DC transmission system has the ability to realize active power and reactive power decoupling control, and can be used to passive networks. Power supply, compact structure, small footprint, no commutation failure, etc., but also have high cost defects. Therefore, combining the advantages of both conventional direct current transmission and flexible direct current transmission, the hybrid DC transmission technology using a thyristor converter at one end converter station and a voltage source converter at the other end converter station has a good engineering application prospect. In the long run, with the reduction of the price of the full control device used in the voltage source converter, the flexible DC transmission technology using the voltage source converter at both ends of the converter station will be more and more widely used.

In order to meet the long-distance and large-capacity transmission demand, the conventional DC transmission project uses two or more thyristor converters in series to improve the DC voltage level and transmission capacity of the DC transmission system. At present, there are many thyristor converters in China. The tandem DC transmission project was completed and put into operation. For the one-end converter station, the thyristor converter is connected in series, the other end of the converter station is connected in series with the voltage source converter, and the series-type hybrid DC transmission technology in which both ends are connected by the voltage source converter. Still in the research stage.

For the DC transmission system using inverter series technology, the requirements of the main circuit topology and control system are to enable online input and online exit of the converter during DC pole operation to meet two or more DC poles. The following requirements are required when the converter is operated in series: 1) The single inverter can be taken out for maintenance on-line, and can be continuously put into operation after the inspection is completed; 2) The online input and exit of the single inverter does not affect the normality of other converters. Operation, the above requirements can ensure the flexibility and reliability of the operation of the series DC transmission system. Current thyristor converter The inverter online return method for series DC transmission systems has matured.

For the series hybrid DC transmission system and the series flexible DC transmission system, if the control method of the thyristor converter series DC transmission system is still used, the voltage source converter is input and exited online, because the voltage source converter has a capacitance. The energy storage component causes a serious fault like the DC side positive pole and the negative pole short circuit of the voltage source converter, which causes the inverter to fail to retract online.

At present, no control method for realizing the online return of the voltage source converter in the series-type DC transmission system has been proposed. Therefore, it is necessary to provide a voltage source converter online with the characteristics of the voltage source converter. The control method and device meet the operation and maintenance requirements of the series hybrid DC transmission system or the series flexible DC transmission system.

Summary of the invention

The object of the present invention is to provide a method and a device for online input and exit control of a voltage source converter unit, which are used for realizing a single operation of two or more converters of a direct current transmission system in a series operation. The online input and exit of the voltage source converter meets the operation and maintenance needs of the series hybrid DC transmission system or the series flexible DC transmission system.

In order to achieve the above object, the technical solution adopted by the present invention is to provide a method for online input control of a voltage source converter unit, wherein the voltage source converter unit includes a first unit isolation knife gate D1 and a voltage source exchanged in series with each other. The flow device, the second unit isolating the knife gate D2 and the connecting wire, the beginning and the end of the series circuit are respectively used as the first DC terminal X1 and the second DC terminal X2 of the voltage source converter unit, respectively, for use with other voltage sources The inverter unit is connected in series; further comprising a unit bypass switch D3 connected between the first DC end point X1 and the second DC end point X2; further comprising a unit bypass switch S1 connected across the Between the near-voltage source converter terminal Y1 of the first unit isolation knife gate D1 and the near-voltage source converter terminal Y2 of the second unit isolation knife gate D2, the online input control method comprises the following steps:

Step 1: Receive the online input command of the voltage source converter unit that is delivered, and close the second unit isolation knife gate D2 to be input into the voltage source inverter unit, so that the negative terminal Z2 of the voltage source converter to be input is input. Connected to the second DC terminal X2 via the second unit isolation knife gate D2;

Step 2: Close the AC incoming line switch S2 of the converter transformer to be input to the voltage source converter unit, charge the inverter to be input to the voltage source converter, and connect the bridge arm submodules of the voltage source converter to be input. The capacitor voltage is charged to a set threshold;

Step 3: Stop the charging control and make the sub-module that is turned on during the charging control process in a locked state. The unit bypass switch S1 and the first unit isolation switch D1 to be input into the voltage source converter unit, and then open the unit bypass switch D3;

Step 4: Unlock the DC voltage U _dV to be input to the voltage source converter and control its output to be 0, then control the negative DC voltage output from the inverter to be input to the voltage source, and increase the negative DC output by the inverter to be input. The magnitude of the voltage causes the DC current flowing through the converter to be input to the voltage source to increase, and the DC current flowing through the unit bypass switch S1 of the inverter unit to be input into the voltage source is reduced, when flowing through the voltage to be input When the DC current value of the source converter is increased to be equal to the DC current measurement value of the operated voltage source converter, the unit bypass switch S1 in the inverter unit to be input to the voltage source is pulled apart;

Step 5: If the converter station where the voltage source converter unit is to be input is a DC voltage control station, control the DC voltage U _dV to be input to the voltage source converter to the operation target value; if the voltage source converter is to be input The converter station where the unit is located is a DC current control station or a DC power control station, and then controls the DC current flowing through the inverter to be input to the operation target value; after that, the input of the voltage source converter unit is completed.

In the step 4 of the above-mentioned voltage source converter unit being put into the line, the method for unlocking the DC voltage U _dV to be input to the voltage source converter and controlling the output thereof is 0, and specifically includes: being a voltage source converter to be input Set the voltage reference wave with zero axis symmetry, equal amplitude and opposite phase for each phase of the upper and lower arms of each arm and unlock.

In the online input process of the above-mentioned voltage source converter unit, the inverter unit is sequentially operated in accordance with the inverter unit that first inputs the DC current control station or the DC power control station, and then the inverter unit that is put into the DC voltage control station. Put into operation online.

The invention also provides an online normal exit control method for a voltage source converter unit, wherein the voltage source converter unit comprises a first unit isolation knife gate D1, a voltage source converter and a second unit isolation knife gate connected in series with each other. D2 and a connecting wire, the beginning and the end of the series circuit respectively serve as a first DC terminal X1 and a second DC terminal X2 of the voltage source converter unit for serial connection with other voltage source converter units; a unit bypass switch D3 connected between the first DC terminal X1 and the second DC terminal X2; further comprising a unit bypass switch S1 spanning the first unit isolation switch D1 Between the near-voltage source converter terminal Y1 and the near-voltage source converter terminal Y2 of the second unit isolation knife gate D2, the online normal exit control method comprises the following steps:

Step 1: Receive the online normal exit command of the converter unit, and control the DC voltage U _{dV of the} output of the converter to be withdrawn to 0;

Step 2: closing the unit bypass switch S1 in the voltage source converter unit to be withdrawn, so that the direct current flowing through the voltage source converter to be withdrawn is transferred to the unit bypass switch S1;

Step 3: Blocking the voltage source converter to be withdrawn, and pulling off the AC incoming line switch S2 of the converter transformer corresponding to the voltage source converter unit;

Step 4: Close the unit bypass switch D3 in the voltage source converter unit to be exited, and then sequentially open the unit bypass switch S1, the first unit isolation knife gate D1, and the second unit isolation knife gate D2, to be withdrawn. The voltage source converter unit exits.

In the online exit process of the voltage source converter unit, the converter unit is sequentially executed according to the converter unit that first exits the DC voltage control station, and then exits the DC current control station or the inverter unit of the DC power control station. The operation exits normally online.

The voltage source converter unit may include an electronic switch K formed by at least one semiconductor switching device, and the electronic switch is coupled between the positive terminal and the negative terminal of the voltage source converter, or coupled to the voltage source for replacement Between the positive terminal and the negative terminal of the streamer sub-module; the conduction direction of the semiconductor switching device of the electronic switch is consistent with the direction of the direct current flowing through the voltage source converter, and is maintained during the normal operation of the voltage source converter In the off state, the semiconductor switching device of the electronic switch is a single semiconductor switching device, or a plurality of semiconductor switching devices are connected in series and/or in parallel. For the voltage source converter unit configured with the electronic switch, step A may be added between step 1 and step 2 of the above-mentioned online normal exit control method: all semiconductors in the electronic switch to be withdrawn from the voltage source converter unit The switching device triggers conduction to provide a current path for the DC current; and between step 3 and step 4, step B is added: latching all semiconductor switching devices in the electronic switch of the inverter unit to be withdrawn from the voltage source.

The invention also provides an online fault exit control method for a voltage source converter unit, wherein the voltage source converter unit comprises a first unit isolation knife gate D1, a voltage source converter and a second unit isolation knife gate connected in series with each other. D2 and a connecting wire, the beginning and the end of the series circuit respectively serve as a first DC terminal X1 and a second DC terminal X2 of the voltage source converter unit for serial connection with other voltage source converter units; a unit bypass switch D3 connected between the first DC terminal X1 and the second DC terminal X2; further comprising a unit bypass switch S1 spanning the first unit isolation switch D1 Between the near-voltage source converter terminal Y1 and the near-voltage source converter terminal Y2 of the second unit isolation knife gate D2, the online fault exit control method comprises the following steps:

Step 1: After detecting the failure of the voltage source inverter unit by detecting the electrical quantity and/or the non-electric quantity, issuing an online fault exit command to the converter unit to be exited;

Step two: blocking the voltage source converter to be withdrawn, and pulling off the AC incoming line switch S2 of the converter transformer corresponding to the voltage source converter unit;

Step 3: Close the unit bypass switch S1 in the voltage source converter unit to be withdrawn, so that the DC current flowing through the inverter to be withdrawn from the voltage source is transferred to the unit bypass switch S1;

For the voltage source converter unit configured with the electronic switch, step A may be added between step 1 and step 2 of the above-mentioned online fault exit control method: all semiconductors in the electronic switch to be withdrawn from the voltage source converter unit The switching device triggers conduction to provide a current path for the DC current; and between step 3 and step 4, step B is added: latching all semiconductor switching devices in the electronic switch of the inverter unit to be withdrawn from the voltage source.

The invention also provides a voltage source converter unit online input device, the voltage source converter unit comprising a first unit isolation knife gate D1, a voltage source converter, a second unit isolation knife gate D2 and Connecting wires, the beginning and the end of the series circuit respectively serving as the first DC terminal X1 and the second DC terminal X2 of the voltage source converter unit for serial connection with other voltage source converter units; a circuit breaker D3 connected between the first DC terminal X1 and the second DC terminal X2; further comprising a unit bypass switch S1 spanning the near voltage of the first unit isolation switch D1 Between the source inverter terminal Y1 and the near-voltage source converter end Y2 of the second unit isolation knife gate D2, the online input device comprises a first sequential connection operation unit, a charging control unit, a second sequential connection operation unit, Unlock the transfer control unit and run the adjustment unit, where:

The first sequence is connected to the operation unit, and the second unit isolation knife gate D2 to be input into the voltage source converter unit is closed, so that the negative terminal Z2 of the voltage source converter to be input is connected to the second unit isolation knife gate D2. Two DC terminal X2, trigger charging control unit;

The charging control unit closes the AC incoming line switch S2 of the converter transformer to be input to the voltage source converter unit, performs charging control on the input voltage source converter, and puts the bridge arms to be input into the voltage source converter The capacitor voltage of the module is charged to a set threshold, and the second sequence is connected to the operation unit;

The second sequence is connected to the operation unit, the charging control is stopped, and the sub-module that triggers the conduction during the charging control process is in a locked state, and the unit bypass switch S1 and the first unit isolation knife to be input into the voltage source inverter unit are closed. Gate D1, and then open the unit bypass knife gate D3, triggering the unlock transfer control unit;

Unlock the transfer control unit, unlock the DC voltage U _dV to be input to the voltage source converter and control its output to 0, then control the negative DC voltage to be input to the voltage source converter, and increase the output of the inverter to be input by the voltage source. The magnitude of the negative DC voltage causes the DC current flowing through the converter to be input to the voltage source to increase, and the DC current flowing through the unit bypass switch S1 of the inverter unit to be input into the voltage source is reduced, when flowing through When the DC current value of the input voltage source converter is increased to be equal to the DC current measurement value of the operated voltage source converter, the unit bypass switch S1 in the inverter unit to be input is pulled, and the operation adjustment is triggered. unit;

The operation adjusting unit, if the converter station where the voltage source converter unit is to be input is a DC voltage control station, controls the DC voltage U _dV to be input to the voltage source converter to the operation target value; if the voltage source to be input is commutated The converter station where the converter unit is located is a DC current control station or a DC power control station, and then controls the DC current flowing through the inverter to be input to the operation target value; after that, the input of the voltage source converter unit is completed.

The unlocking transfer control unit further includes a zero voltage unlocking unit, and the zero voltage unlocking unit sets a voltage reference wave with 0 axis symmetry, equal amplitude, and opposite phase for the upper and lower arms of each phase of the voltage source converter to be input. And unlocking, so that the DC voltage U _dV to be input to the voltage source converter is 0.

The invention also provides a voltage source converter unit online exit device, the voltage source converter unit comprising a first unit isolation knife gate D1, a voltage source converter, a second unit isolation knife gate D2 and Connecting wires, the beginning and the end of the series circuit respectively serving as the first DC terminal X1 and the second DC terminal X2 of the voltage source converter unit for serial connection with other voltage source converter units; a circuit breaker D3 connected between the first DC terminal X1 and the second DC terminal X2; further comprising a unit bypass switch S1 spanning the near voltage of the first unit isolation switch D1 Between the source converter terminal Y1 and the near-voltage source converter terminal Y2 of the second unit isolation knife gate D2, the online exit device includes a DC voltage reduction control unit, a bypass transfer control unit, and an inverter lock control unit. , the knife sequence operation unit, wherein:

The online normal exit operation works as follows:

The DC voltage reduction control unit controls the DC voltage U _{d of the} output of the converter to be withdrawn from the voltage source to drop to 0, and triggers the bypass transfer control unit;

The bypass transfer control unit closes the unit bypass switch S1 to be withdrawn from the voltage source converter unit, so that the direct current flowing through the inverter to be withdrawn from the voltage source is transferred to the unit bypass switch S1, triggering the inverter to block control unit;

The converter locks the control unit, locks the voltage source converter to be withdrawn, and pulls off the AC inlet switch S2 of the converter transformer corresponding to the voltage source converter unit to be triggered, and triggers the knife sequence operation unit;

The knife gate sequence operation unit closes the unit bypass knife switch D3 in the voltage source converter unit, and then sequentially opens the unit bypass switch S1, the first unit isolation knife gate D1, and the second unit isolation knife gate D2. The exit of the voltage source converter unit is to be completed.

The online fault exit operation works as follows:

The converter locks the control unit, locks the voltage source converter to be withdrawn, and pulls off the AC incoming line switch S2 of the converter transformer corresponding to the voltage source converter unit to trigger the bypass transfer control unit;

Bypass transfer control unit, close the unit bypass switch S1 in the voltage source converter unit to be exited The DC current exiting the voltage source converter is transferred to the unit bypass switch S1 to trigger the knife sequence operation unit;

For the voltage source converter unit configured with the electronic switch, the above-mentioned online exit device further includes an electronic switch control unit for triggering all semiconductor switching devices in the electronic switch to be withdrawn from the voltage source converter unit to be turned into a direct current The current provides a current path and latches all of the semiconductor switching devices in the electronic switch to be withdrawn from the voltage source converter unit.

The beneficial effects of the invention are:

The control method and device proposed by the invention can realize the online smooth input and exit of the voltage source converter in the series hybrid DC transmission system or the series type flexible direct current transmission system, and does not affect the normal and stable operation of other operated converters.

DRAWINGS

1 is a topological structural view of a voltage source converter unit in the present invention;

2 is a schematic diagram of a main circuit of a two-pole series hybrid DC transmission system using a voltage source converter unit of the present invention;

3 is a schematic diagram of a main circuit of a two-pole series type flexible direct current transmission system using a voltage source converter unit of the present invention;

4 is a topological schematic diagram of a voltage source converter in a voltage source converter unit of the present invention, wherein each of the upper and lower arm of each phase may be cascaded by a first type of submodule, or both of the first submodules And a second type of sub-module mixed cascade;

5 is a schematic diagram showing a state in which a voltage source converter unit and a voltage source converter unit to be input are started before the online input operation is started in the present invention;

6 is a schematic diagram of a state of a DC side of an already operated voltage source converter unit and a voltage source converter unit to be input before starting a DC current transfer process according to the present invention;

7 is a waveform diagram of voltage reference waves outputted by three-phase upper and lower arms when the output source DC voltage of the voltage source converter is 0 in the voltage source converter unit of the present invention;

8 is a waveform diagram of a three-phase AC voltage when a DC voltage output of a voltage source converter is 0 in a voltage source converter unit of the present invention;

Figure 9 is a topological structural view of a parallel electronic switch between a positive terminal and a negative terminal of a voltage source converter in the present invention;

10 is a topological structural view of a parallel electronic switch between a positive terminal and a negative terminal of a voltage source converter sub-module in the present invention;

11 is a flow chart of a method for online input and exit control of a voltage source converter unit in the present invention.

detailed description

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

The invention provides a voltage source converter unit control method, which is used for realizing online input and online exit of a single voltage source converter when two or more converters of a direct current transmission system have two or more converters connected in series, which can satisfy the series connection. Operation and maintenance of a hybrid HVDC system or a series HVDC system.

In order to achieve the above object, the solution of the present invention is to provide a voltage source converter unit control method for realizing online input of a voltage source converter unit during DC pole operation, the voltage source converter unit The topological structure is as shown in FIG. 1 , which includes a first unit isolation knife gate D1 , a voltage source converter, a second unit isolation knife gate D2 and a connecting wire connected in series, and the starting end and the end of the series circuit respectively serve as the voltage source. a first DC terminal X1 and a second DC terminal X2 of the inverter unit for serial connection with other voltage source inverter units; further comprising a unit bypass switch D3 connected across the first DC Between the terminal X1 and the second DC terminal X2; further comprising a unit bypass switch S1 spanning the near-voltage source converter terminal Y1 and the second unit isolation blade gate D2 of the first unit isolation blade D1 Near the voltage source converter end Y2. The main circuit of the two-pole series hybrid DC transmission system using the voltage source converter unit is as shown in FIG. 2, and the main circuit of the two-pole series flexible DC transmission system at both ends of the voltage source converter unit is adopted. As shown in Figure 3.

The voltage source converter in the above voltage source converter unit adopts a modular multi-level structure as shown in FIG. 4 and includes the following two types or one type of sub-modules:

The first type of sub-module is a sub-module capable of outputting positive, negative, and zero-level levels in a non-blocking state, such as a full bridge submodule FBSM.

The second type of sub-module is a sub-module that can output only positive and zero levels in the non-blocking state, such as a half-bridge sub-module HBSM, a full-bridge sub-module SFBSM, and the like.

The sub-module includes fully-controlled switching devices such as IGBT, IGCT, IEGT, GTO, and the like.

The sub-module configuration manner of the bridge arm of the voltage source converter in the above voltage source converter unit includes the following two types:

In the first method, the upper and lower arms of each phase are cascaded by the first type of sub-modules.

In the second mode, each of the upper and lower bridge arms is divided into two types: the first type submodule and the second type submodule. The number of the configuration is cascaded to form a hybrid bridge arm, and the number of the two sub-modules of each bridge arm is the same; the second method reduces the number of the first type of sub-modules in the voltage source inverter arm, and reduces the voltage. The design cost and operating loss of the source converter have higher engineering application value.

Before the online input operation is started, the state of the voltage source converter unit and the voltage source converter unit to be input is shown in FIG. 5, and the first unit isolation knife gate D1 to be input to the voltage source converter unit The two-unit isolation knife gate D2, the unit bypass switch S1 and the AC inlet switch S2 are all in the position, and the unit bypass knife gate D3 is in the position.

The online input control method of the voltage source converter unit in the present invention is as shown in FIG. 11 , and specifically includes the following steps:

Step 2: Close the AC incoming line switch S2 corresponding to the commutation variable to be input to the voltage source converter unit, first treat the input voltage source converter for AC uncontrolled charging, and then set a value close to the rated value as the threshold. And starting the charging control to charge the capacitor voltage of each bridge arm sub-module of the voltage source converter to a set threshold;

Step 3: Stop the charging control, and make the sub-module that is turned on during the charging control process in a locked state, close the unit bypass switch S1 and the first unit isolation knife gate D1 to be input into the voltage source converter unit, and then Pull the unit bypass knife switch D3.

After the completion of step three, it is necessary to start the unlocking and DC current transfer process of the inverter unit to be input, first unlocking the inverter to be input and outputting the DC voltage U _dV to 0; before starting the DC current transfer process, The DC side state of the operated voltage source converter unit and the voltage converter unit to be input is shown in Fig. 6. At this time, I _d1 is equal to I _d and I _d2 is equal to 0, where I _d is the flow voltage that has passed through the operation. The DC current of the inverter unit and the converter unit to be input to the voltage source, I _d1 is the DC current flowing through the unit bypass switch S1 in the inverter unit to be input to the voltage source, and I _d2 is the source of the voltage to be input. DC current of the converter.

For the converter unit to be input to the voltage source, I _d = I _d1 + I _d2 can be obtained according to Kirchhoff's current law.

In order to realize the transition of the DC current from the unit bypass switch S1 to the voltage source converter to be input, it is necessary to increase I _d2 and decrease I _d1 until the DC current I _d remains unchanged until I _d2 rises to I _{d is} equal and I _d1 drops to zero.

It is studied that the DC-side control characteristic of the converter to be input to the voltage source can be equivalent to a controlled voltage source U _S and a resistor R. The DC current transfer loop to be input into the voltage source converter unit can be equivalent to a graph. The closed loop formed by a controlled voltage source, a resistor and the unit bypass switch S1 connected in series 6 controls the controlled voltage source U _S corresponding to the input voltage source converter to output a negative DC voltage, which can be this produces a closed loop in opposite I _d1 flowing current I _d2, as the source voltage to be input to the inverter corresponding to the output controlled voltage source U _S increased negative DC voltage magnitude, I _d2 gradually increases, the I _D1 gradually decreases. When I _d2 rises to be equal to I _d , I _d1 drops to 0. At this time, the unit bypass switch S1 is pulled to complete the DC current transfer process, and the following subsequent steps of step 3 can be obtained correspondingly:

Step 4: Unlock the DC voltage U _dV to be input to the voltage source converter and control its output to 0, and then control the negative DC voltage output from the inverter to be input to the voltage source, and gradually increase the output of the inverter to be input by the voltage source. The amplitude of the DC voltage causes the DC current flowing through the converter to be input to the voltage source to gradually increase, and the DC current flowing through the unit bypass switch S1 gradually decreases, when flowing through the DC current to be input to the voltage source converter When the value is increased to be equal to the DC current measurement value of the operated voltage source converter, the unit bypass switch S1 in the inverter unit to be input to the voltage source is pulled apart;

The method for unlocking the DC voltage U _dV to be input to the voltage source converter and controlling the output thereof is 0, and specifically includes: setting a DC voltage reference value U _dV of the inverter to be input in the constant voltage control mode. _Ref is 0 and unlocked. At this time, the voltage source converter is to be input to the voltage reference wave of each phase of the upper and lower arm of each phase, and the amplitude is equal and the phase is opposite. The waveform is shown in Fig. 7, where U _{an- Ref} , U _bn-ref , U _cn-ref are the voltage reference waves of the three-phase lower arm of the inverters A, B and C to be input, respectively, U _ap-ref , U _bp-ref , U _cp-ref respectively For the voltage reference wave of the three-phase upper arm of the converter A, B, C to be input to the voltage source, U _dV is the DC voltage to be input to the converter of the voltage source, and U _dV-ref is the inverter to be input to the voltage source The DC voltage reference value; at this time, the three-phase AC voltage waveform corresponding to the voltage source converter to be input is shown in Fig. 8, wherein U _a , U _b , and U _c are AC voltages of three phases A, B, and C, respectively.

Step 5: If the converter station where the voltage source converter unit is to be input is a DC voltage control station, the control mode of the converter to be input to the voltage source is maintained as a constant voltage control mode and its DC voltage reference value U _{dV- The ref} ramps up to the running target value at a certain rate. Under the action of the DC voltage controller, the DC voltage U _dV outputted by the voltage source converter also ramps up to the running target value at a certain rate; if the voltage source to be input is commutated The converter station where the converter unit is located is a DC current control station or a DC power control station, and the control mode of the converter to be input to the voltage source is smoothly switched to the constant current control mode and the DC current reference value is set to the DC pole. The DC current running target value is adjusted by the DC current controller, and the DC current flowing through the voltage source converter is adjusted to the DC current running target value of the DC pole; after that, the input of the voltage source converter unit is completed.

For the two-terminal DC transmission system, the control mode usually adopted is that one end converter station controls DC current or DC power, and the other end converter station controls DC voltage. The two ends cooperate to maintain the DC transmission power at the target value, and the control mode can be in two. The conversion between the converter stations is carried out.

In the online input process of the voltage source converter unit, the converter unit is first put into the converter unit of the DC current control station or the DC power control station, and then the converter unit of the DC voltage control station is input. Put into operation online.

The invention also provides an online normal exit control method for a voltage source converter unit, wherein the voltage source converter unit comprises a first unit isolation knife gate D1, a voltage source converter and a second unit isolation knife gate connected in series with each other. D2 and a connecting wire, the beginning and the end of the series circuit respectively serve as a first DC terminal X1 and a second DC terminal X2 of the voltage source converter unit for serial connection with other voltage source converter units; a unit bypass switch D3 connected between the first DC terminal X1 and the second DC terminal X2; further comprising a unit bypass switch S1 spanning the first unit isolation switch D1 The near-voltage source converter Y1 and the near-voltage source converter terminal Y2 of the second unit isolation knife gate D2, the online normal exit control method is as shown in FIG. 11, and specifically includes the following steps:

Step 1: Receive the online normal exit command of the converter unit. If the converter station where the voltage source converter unit is to be exited is the DC voltage control station, the control mode of the converter to be exited from the voltage source remains unchanged. The voltage control mode and the DC voltage reference value U _dV-ref are ramped down to 0 at a certain rate, and the DC voltage U _dV outputted by the voltage source converter is also ramped down at a certain rate under the action of the DC voltage controller. To 0; if the converter station where the voltage source converter unit is to be exited is a DC current control station or a DC power control station, the control mode of the converter to be withdrawn from the voltage source is firstly switched from the constant current control mode to the constant voltage. The control mode and the DC voltage reference value U _dV-ref are ramped down to 0 at a certain rate, and the DC voltage U _dV outputted by the voltage source converter is ramped down to a certain rate under the action of the DC voltage controller. 0, when the DC voltage reference value falls to 0, the upper and lower arms of each phase of the inverter to be withdrawn from the voltage source output a voltage reference wave with zero axis symmetry, equal amplitude and opposite phase, which is to be withdrawn Voltage source inverter output direct voltage U _dV is 0.

Step 3: Blocking the voltage source converter to be withdrawn and pulling off the AC incoming line switch S2 of the converter transformer corresponding to the voltage source converter unit;

Step 4: Close the unit bypass switch D3 in the voltage source converter unit to be exited, and then sequentially open the unit bypass switch S1, the first unit isolation knife gate D1, and the second unit isolation knife gate D2. Exit the electrical isolation of the voltage source converter, and exit the voltage source converter unit to exit.

During the online withdrawal process of the voltage source converter unit, the converter unit is first exited from the DC voltage control station, and then the inverter unit of the DC current control station or the DC power control station is sequentially discharged. In Line exit operation.

When the voltage source converter fails, the fully-controlled switching device of the voltage source converter needs to be quickly blocked to isolate the fault, which causes the voltage source converter to lose normal control capability, and cannot be controlled by the above-mentioned online normal exit control method. The online fault of the voltage source converter exits. To this end, the present invention also provides a voltage source converter unit online fault exit control method, the voltage source converter unit includes a first unit isolation knife gate D1, a voltage source converter, and a second unit connected in series with each other. Isolating the knife gate D2 and the connecting wire, the beginning and the end of the series circuit respectively serve as the first DC terminal X1 and the second DC terminal X2 of the voltage source converter unit, respectively, for serial connection with other voltage source converter units Also included is a unit bypass switch D3 that is connected between the first DC terminal X1 and the second DC terminal X2; and a unit bypass switch S1 that is connected across the first unit isolation blade The near-voltage source converter terminal Y1 of the gate D1 and the near-voltage source converter terminal Y2 of the second unit isolation knife gate D2 are as shown in FIG. 11 , and specifically include the following steps:

According to the online fault exit control method described above, a certain degree of overvoltage occurs before the unit bypass switch S1 in the voltage source converter unit to be withdrawn is closed. It has been studied that the configuration of the electronic switch K in the voltage source converter unit can effectively avoid the overvoltage problem during the online fault exit process, and the electronic switch is coupled between the positive terminal and the negative terminal of the voltage source converter, or And connected between the positive terminal and the negative terminal of the voltage source converter sub-module; the conduction direction of the semiconductor switching device of the electronic switch is consistent with the direction of the direct current flowing through the voltage source converter, and the voltage source is commutated The semiconductor switching device of the electronic switch is a single semiconductor switching device, or a plurality of semiconductor switching devices are connected in series and/or in parallel; the semiconductor switching device is a semi-controlled switching device, such as Thyristor SCR, or fully controlled switching devices such as IGBT, IGCT, IEGT, GTO, etc. The structure of the electronic switch coupled between the positive terminal and the negative terminal of the voltage source converter is as shown in FIG. 9; the electronic switch is coupled between the positive terminal and the negative terminal of the voltage source converter submodule The structure is shown in Figure 10.

In practical engineering applications, one phase can be selected among the three-phase bridge arms of the voltage source converter, and the sub-modules of the upper and lower arms are configured with electronic switches, and the other two phases are not configured to reduce the semiconductor switching device. usage amount.

It should be noted that for a series-type flexible direct current transmission system in which a direct current can flow bidirectionally, two sets of electronic switches can be configured in an anti-parallel manner to ensure that voltage can be realized in both forward and reverse current directions. The source converter unit exits online.

For the voltage source converter unit configured with the electronic switch, step A may be added between step 1 and step 2 of the above-mentioned voltage source converter unit online fault exit control method: the voltage source converter unit to be withdrawn All of the semiconductor switching devices in the electronic switch trigger the conduction to provide a current path for the direct current; and between step three and step four, step B is performed: latching all the semiconductor switching devices in the electronic switch of the inverter unit to be withdrawn from the voltage source. After the above steps are added, the overvoltage problem during the online fault exit process can be effectively avoided.

In addition, for the voltage source converter unit configured with the electronic switch, step A may be added between step 1 and step 2 of the online normal converter control method of the voltage source converter unit: commutating the voltage source to be withdrawn All semiconductor switching devices in the electronic switch of the unit are triggered to provide a current path for the direct current; and between step 3 and step four, step B is added: blocking all semiconductor switching devices in the electronic switch of the inverter unit to be withdrawn from the voltage source The technical advantage of adding the above steps is that it can ensure that the unit bypass switch S1 of the voltage source converter unit to be withdrawn in step 2 is closed, and the DC voltage U _dV outputted by the front voltage source converter is 0, so that the unit is bypassed. Switch S1 has a good closing condition.

The charging control unit closes the AC incoming line switch S2 of the converter transformer to be input to the voltage source converter unit, performs charging control on the input voltage source converter, and puts the bridge arms to be input into the voltage source converter Module power The capacitor voltage is charged to the set threshold, and the second sequence is connected to the operation unit;

Unlock the transfer control unit, unlock the DC voltage U _dV to be input to the voltage source converter and control its output to 0, then control the negative DC voltage to be input to the voltage source converter, and gradually increase the inverter to be input. The amplitude of the negative DC voltage is output, so that the DC current flowing through the converter to be input to the voltage source is gradually increased, and the DC current flowing through the unit bypass switch S1 is gradually decreased, when flowing through the converter to be input to the voltage source When the DC current value is increased to be equal to the DC current measurement value of the operated voltage source converter, the unit bypass switch S1 in the inverter unit to be input is pulled, and the operation adjustment unit is triggered;

The unlocking transfer control unit further includes a zero voltage unlocking unit that sets the DC voltage reference value U _dV-ref to be input to the voltage source converter to 0 and unlocks, and is to be input to the voltage source converter The voltage reference wave with zero axis symmetry, equal amplitude and opposite phase is outputted on each of the upper and lower arms of each phase, and the DC voltage U _dV to be input to the voltage source converter is 0.

The online normal exit operation works as follows:

The online fault exit operation works as follows:

The bypass transfer control unit closes the unit bypass switch S1 to be withdrawn from the voltage source converter unit, so that the direct current flowing through the inverter to be withdrawn from the voltage source is transferred to the unit bypass switch S1, triggering the sequence operation of the switch unit;

The above embodiments are only for explaining the technical idea of the present invention, and the scope of protection of the present invention is not limited thereto. Any modification made based on the technical idea according to the technical idea of the present invention falls within the protection scope of the present invention. Inside.

Claims

A voltage source converter unit online input control method, the voltage source converter unit includes a first unit isolation knife gate (D1), a voltage source converter, and a second unit isolation knife gate (D2) connected in series with each other And connecting wires, the beginning and the end of the series circuit respectively serving as a first DC terminal (X1) and a second DC terminal (X2) of the voltage source converter unit, respectively, for serial connection with other voltage source converter units Also included is a unit bypass switch (D3) that is connected across the first DC terminal (X1) and the second DC terminal (X2); and includes a unit bypass switch (S1) that is bridged Between the near-voltage source converter end (Y1) of the first unit isolation knife gate (D1) and the near-voltage source converter end (Y2) of the second unit isolation knife gate (D2), characterized in that The online input control method includes the following steps:

Step 1: Receive the online input command of the voltage source converter unit that is delivered, and close the second unit isolation knife gate (D2) to be input into the voltage source converter unit, so that the voltage source converter is to be input negative. The terminal (Z2) is connected to the second DC terminal (X2) via the second unit isolation knife gate (D2);

Step 2: Close the AC incoming line switch (S2) of the converter transformer to be input to the voltage source converter unit, charge the inverter to be input to the voltage source, and connect the bridges of the voltage source converter to be input. The capacitor voltage of the submodule is charged to a set threshold;

Step 3: Stop the charging control, and make the sub-module that is turned on during the charging control process in a locked state, and close the unit bypass switch (S1) and the first unit isolation knife gate to be input into the voltage source converter unit ( D1), and then open the unit bypass switch (D3);

Step 4: Unlock the DC voltage (U dV ) to be input to the voltage source converter and control its output to 0. Then control the inverter to be input to the voltage source to output a negative DC voltage, and increase the inverter to be input. The amplitude of the negative DC voltage is output, so that the DC current flowing through the converter to be input to the voltage source is increased, and the DC current flowing through the unit bypass switch (S1) in the inverter unit to be input into the voltage source is reduced. The DC current is transferred from the unit bypass switch (S1) to the inverter to be input to the voltage source, and the DC current flowing through the converter to be input to the voltage source is increased to the DC current measurement with the inverter of the operated voltage source. When the values are equal, pull out the unit bypass switch (S1) to be input into the voltage source converter unit;

Step 5: If the converter station where the voltage source converter unit is to be input is a DC voltage control station, control the DC voltage (U dV ) to be input to the voltage source converter to the operation target value; The converter station where the flow unit is located is a DC current control station or a DC power control station, and then controls the DC current flowing through the inverter to be input to the operation target value; after that, the input of the voltage source converter unit is completed.
The online input control method for a voltage source converter unit according to claim 1, wherein: in step 4, the unlocking a DC voltage (U dV ) to be input to the voltage source converter and controlling the output thereof is implemented. The method of 0 specifically includes: setting a voltage reference wave with zero-axis symmetry, equal amplitude, and opposite phase for each phase of the upper and lower arms of the inverter to be input to the voltage source converter and unlocking.
The online input control method for a voltage source converter unit according to claim 1, wherein in the online input process of the voltage source converter unit, the DC current control station or the DC power control station is first input. The inverter unit and the inverter unit that is reintroduced into the DC voltage control station are sequentially operated in the inverter unit.
A voltage source converter unit online normal exit control method, the voltage source converter unit comprises a first unit isolation knife gate (D1), a voltage source converter, and a second unit isolation knife gate (D2) connected in series with each other And a connecting wire, the beginning and the end of the series circuit respectively serving as a first DC terminal (X1) and a second DC terminal (X2) of the voltage source converter unit, respectively, for performing with other voltage source converter units In series; further comprising a unit bypass switch (D3) connected between the first DC end point (X1) and the second DC end point (X2); further comprising a unit bypass switch (S1) spanning Between the near-voltage source converter end (Y1) of the first unit isolation knife gate (D1) and the near-voltage source converter end (Y2) of the second unit isolation knife gate (D2), characterized The method of the online normal exit control includes the following steps:

Step 1: receiving the online normal voltage exit unit of the voltage source converter, and controlling the DC voltage (U dV ) of the output of the converter to be withdrawn from the voltage source to drop to 0;

Step 2: Close the unit bypass switch (S1) to be withdrawn from the voltage source converter unit, and transfer the DC current flowing through the inverter to be withdrawn to the unit bypass switch (S1);

Step 3: Blocking the voltage source converter to be withdrawn, and pulling off the AC incoming line switch (S2) of the converter transformer corresponding to the voltage source converter unit;

Step 4: Close the unit bypass switch (D3) in the voltage source converter unit to be exited, and then sequentially open the unit bypass switch (S1), the first unit isolation switch (D1), and the second unit isolation. Knife gate (D2), the voltage source converter unit to be exited is completed.
The on-line normal exit control method for a voltage source converter unit according to claim 4, characterized in that: in the online exit process of the voltage source converter unit, according to the converter that first exits the DC voltage control station The order of the inverter unit of the unit, and then exiting the DC current control station or the DC power control station performs an online exit operation of the inverter unit.
The on-line normal exit control method for a voltage source converter unit according to claim 4, wherein the voltage source converter unit further comprises an electronic switch (K) formed by at least one semiconductor switching device, the electronic switches being connected in parallel Connected between the positive terminal and the negative terminal of the voltage source converter, or coupled between the positive terminal and the negative terminal of the voltage source converter sub-module; the conduction direction and flow direction of the semiconductor switching device of the electronic switch The direct current direction of the voltage source converter is uniform, and is kept in an off state during normal operation of the voltage source converter, and the semiconductor switching device of the electronic switch is a single semiconductor switching device, or a plurality of semiconductor switching devices are connected in series and And/or in parallel, characterized in that: during the normal exit process of the voltage source converter unit, step A and step two are further included in step A: all semiconductors in the electronic switch to be withdrawn from the voltage source converter unit The switching device triggers conduction to provide a current path for the direct current;

Between step three and step four, step B is further included: latching all semiconductor switching devices in the electronic switch to be withdrawn from the voltage source converter unit.
A voltage source converter unit online fault exit control method, the voltage source converter unit comprises a first unit isolation knife gate (D1), a voltage source converter, and a second unit isolation knife gate (D2) connected in series And a connecting wire, the beginning and the end of the series circuit respectively serving as a first DC terminal (X1) and a second DC terminal (X2) of the voltage source converter unit, respectively, for performing with other voltage source converter units In series; further comprising a unit bypass switch (D3) connected between the first DC end point (X1) and the second DC end point (X2); further comprising a unit bypass switch (S1) spanning Between the near-voltage source converter end (Y1) of the first unit isolation knife gate (D1) and the near-voltage source converter end (Y2) of the second unit isolation knife gate (D2), characterized The method of the online fault exit control includes the following steps:

Step 1: After detecting the failure of the voltage source inverter unit by detecting the electrical quantity and/or the non-electric quantity, issuing an online fault exit command to the converter unit to be exited;

Step 2: Blocking the voltage source converter to be withdrawn, and pulling off the AC incoming line switch (S2) of the converter transformer corresponding to the voltage source converter unit to be withdrawn;

Step 3: Close the unit bypass switch (S1) to be withdrawn from the voltage source converter unit, and transfer the DC current flowing through the voltage source converter to the unit bypass switch (S1);

Step 4: Close the unit bypass switch (D3) in the voltage source converter unit to be exited, and then sequentially open the unit bypass switch (S1), the first unit isolation switch (D1), and the second unit isolation. Knife gate (D2), the voltage source converter unit to be exited is completed.
A voltage source converter unit online fault exit control method according to claim 7, wherein said voltage source converter unit further comprises an electronic switch (K) formed by at least one semiconductor switching device, said electronic switch being coupled Between the positive terminal and the negative terminal of the voltage source converter, or coupled between the positive terminal and the negative terminal of the voltage source converter sub-module; the conduction direction and the voltage of the semiconductor switching device of the electronic switch Source converter DC current direction And maintaining the off state during normal operation of the voltage source converter, the semiconductor switching device of the electronic switch is a single semiconductor switching device, or a plurality of semiconductor switching devices are connected in series and / or in parallel, characterized in that: In the online fault exit process of the voltage source converter unit, step A and step two are further included in step A: triggering all semiconductor switching devices in the electronic switch of the voltage source converter unit to be turned off to provide direct current supply. a current channel;

Between step three and step four, step B is further included: latching all semiconductor switching devices in the electronic switch to be withdrawn from the voltage source converter unit.
A voltage source converter unit is connected to a line device, and the voltage source converter unit includes a first unit isolation knife gate (D1), a voltage source converter, and a second unit isolation knife gate (D2) connected in series with each other. a connecting wire, the first end and the end of the series circuit respectively serving as a first DC terminal (X1) and a second DC terminal (X2) of the voltage source converter unit for serial connection with other voltage source converter units; Also included is a unit bypass switch (D3) that is connected across the first DC terminal (X1) and the second DC terminal (X2); further includes a unit bypass switch (S1) that is connected across The near-voltage source converter end (Y1) of the first unit isolation knife gate (D1) and the near-voltage source converter end (Y2) of the second unit isolation knife gate (D2) are characterized by:

The online input device includes a first sequential connection operation unit, a charging control unit, a second sequential connection operation unit, an unlock transfer control unit, and an operation adjustment unit, wherein:

The first sequence is connected to the operation unit, and the second unit isolation knife gate (D2) to be input into the voltage source converter unit is closed, so that the negative terminal (Z2) of the voltage source converter to be input is passed through the second unit isolation knife gate. (D2) connected to the second DC terminal (X2) to trigger the charging control unit;

The charging control unit closes the AC incoming line switch (S2) of the converter transformer to be input to the voltage source converter unit, performs charging control on the input voltage source converter, and connects the bridges to be input to the voltage source converter The capacitor voltage of the arm module is charged to a set threshold, and the second sequence is connected to the operation unit;

The second sequence is connected to the operation unit, the charging control is stopped, and the sub-module that triggers the conduction during the charging control is in a locked state, and the unit bypass switch (S1) and the first unit to be input into the voltage source converter unit are closed. Isolation knife switch (D1), then open the unit bypass knife gate (D3), trigger the unlock transfer control unit;

Unlock the transfer control unit, unlock the DC voltage (U dV ) to be input to the voltage source converter and control its output to 0, then control the negative DC voltage to be input to the voltage source converter, and increase the commutation of the voltage source to be input. The output of the negative DC voltage is increased, so that the DC current flowing through the converter to be input to the voltage source is increased, and the DC current flowing through the unit bypass switch (S1) in the inverter unit to be input to the voltage source is reduced. When the value of the direct current flowing through the converter to be input to the voltage source is increased to be equal to the measured value of the direct current of the operated voltage source converter, the unit bypass switch in the inverter unit to be input is pulled ( S1), triggering the operation adjustment unit;

The operation adjusting unit, if the converter station where the voltage source converter unit is to be input is a DC voltage control station, controls the DC voltage (U dV ) to be input to the voltage source converter output to the operation target value; The converter station where the converter unit is located is a DC current control station or a DC power control station, and then controls the DC current flowing through the converter of the voltage source to be input to the operation target value; after that, the inverter unit to be input is completed. .
The voltage source inverter unit online input device according to claim 9, wherein the unlocking transfer control unit further comprises a zero voltage unlocking unit, and the zero voltage unlocking unit is a voltage source converter to be input. The upper and lower arms of each phase are set with zero-axis symmetrical, equal-amplitude and opposite-phase voltage reference waves and unlocked, so that the DC voltage (U dV ) to be input to the voltage source converter is zero.
A voltage source converter unit is an online exit device, and the voltage source converter unit includes a first unit isolation knife gate (D1), a voltage source converter, and a second unit isolation knife gate (D2) connected in series with each other. a connecting wire, the first end and the end of the series circuit respectively serving as a first DC terminal (X1) and a second DC terminal (X2) of the voltage source converter unit for serial connection with other voltage source converter units; Also included is a unit bypass switch (D3) that is connected across the first DC terminal (X1) and the second DC terminal (X2); further includes a unit bypass switch (S1) that is connected across The near-voltage source converter end (Y1) of the first unit isolation knife gate (D1) and the near-voltage source converter end (Y2) of the second unit isolation knife gate (D2) are characterized by:

The online exit device includes a DC voltage reduction control unit, a bypass transfer control unit, an inverter lock control unit, and a knife sequence operation unit, wherein:

The online normal exit operation works as follows:

The DC voltage reduction control unit controls the DC voltage (U d ) of the output of the converter to be withdrawn from the voltage source to drop to 0, triggering the bypass transfer control unit;

Bypass transfer control unit, close the unit bypass switch (S1) to be withdrawn from the voltage source converter unit, and transfer the DC current flowing through the voltage source converter to the unit bypass switch (S1), triggering Inverter lockout control unit;

The converter locks the control unit, locks the voltage source converter to be withdrawn, and pulls off the AC inlet switch (S2) of the converter transformer corresponding to the voltage source converter unit to be triggered, and triggers the knife sequence operation unit;

The knife gate sequence operation unit, close the unit bypass knife gate (D3) to be withdrawn from the voltage source converter unit, and then sequentially open the unit bypass switch (S1), the first unit isolation knife gate (D1), the first Two-unit isolation knife gate (D2), the exit of the voltage source converter unit to be exited is completed;

The online fault exit operation works as follows:

The converter locks the control unit, locks the voltage source converter to be withdrawn, and pulls off the AC incoming line switch (S2) of the converter transformer corresponding to the voltage source converter unit to be triggered, and triggers the bypass transfer control unit;

Bypass transfer control unit, close the unit bypass switch (S1) to be withdrawn from the voltage source converter unit, and transfer the DC current flowing through the voltage source converter to the unit bypass switch (S1), triggering Knife gate sequence operating unit;

The knife gate sequence operation unit, close the unit bypass knife gate (D3) to be withdrawn from the voltage source converter unit, and then sequentially open the unit bypass switch (S1), the first unit isolation knife gate (D1), the first The two-unit isolation knife gate (D2) is to be withdrawn from the voltage source converter unit.
A voltage source converter unit in-line exit device according to claim 11, said voltage source converter unit further comprising an electronic switch (K) formed by at least one semiconductor switching device coupled to the voltage Between the positive terminal and the negative terminal of the source converter, or coupled between the positive terminal and the negative terminal of the voltage source converter sub-module; the conduction direction of the semiconductor switching device of the electronic switch is changed with the voltage source The direct current direction of the flow device is uniform and remains in an off state during normal operation of the voltage source converter, the semiconductor switching device of the electronic switch is a single semiconductor switching device, or a plurality of semiconductor switching devices are connected in series and/or in parallel The utility model is characterized in that it comprises an electronic switch control unit for triggering all semiconductor switching devices in the electronic switch to be withdrawn from the voltage source converter unit to provide a current channel for direct current, and to lock the voltage source converter to be withdrawn. All semiconductor switching devices in the unit's electronic switch.